Simulation of macropore growth for photonic crystals

With the aid of techniques developed in the group. The student will develop MATLAB (or alternatuve) coding for the simulation of pore groth and its modulation during the fabrication process. Results of simulation will be compared with the characteristics of samples fabricated in the laboratory.During the last years, photonic crystals have attracted much attention due to their promising characteristic in optical applications. This interest has spurred the research of complex structured materials in order to obtain the desired optical behaviour. Generally speaking, the functionality of photonic crystal depends on their macroscopic structure (albeit of nanometre sized features) such as thin layer stacks. Nevertheless, the design and fabrication of a photonic crystal normally requires many process steps. Recently a new type of photonic crystal has emerged in the form of macroporous silicon. This new material is based on a fabrication method that creates structures by etching or carving holes in a silicon substrate: the pores. This has several advantages, and one way to obtain the highest quality photonic crystals is using the electrochemical etching of silicon wafers. Electrochemical dissolution is deceptively simple on the surface, there are just a handful of parameters to control the etching process: mainly bias, current, electrolyte concentration, and temperature. However, electrochemical processes are one of the most complex phenomena to describe in nowadays knowledge: even more, it is not yet fully understood. This complexity arises from the many interrelated processes taking place in an electrochemical cell. Some simple model have been developed trying to explain and determine the behaviour of the maropore formation during the etching of silicon. The most common model being the one developed by Lehmann. Nevertheless these models are incomplete and necessarily make many simplifying assumptions. As a consequence, the fabrication of macroporous silicon structures using electrochemical etching, often requires much fine tuning by trial and error, resulting in many wasted time and material. The work presented in this master thesis is oriented to develop a simulation tool. Emphasis is made in the numerical simulation of the dynamic evolution of the pore growth. The main interest is being able to reduce the turn-around time to the fabrication of a to-specs photonic crystal, cost savings, reduced waste, and gaining insight on the growth mechanisms in order to produce the next generation, smaller scale macroporous silicon photonic crystals